This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-248096, filed on Aug. 17, 2001: the entire contents of which are incorporated herein by reference.
This invention relates to a thermal transfer printing method and a printer system for printing face images for recognizing individuals and character images such as individual information on recording media.
So far, a sublimation dye transfer printing method is available as a main stream of methods for printing face images on image display media containing face images for recognizing individuals such as, for example, driver""s licenses, passports, credit cards, membership cards and so forth. This sublimation dye transfer printing method is to make the sublimation transfer printing of desired images on printing media by superimposing a thermal transfer ribbon having sublimation (or heat migration) dyes coated on a film-shaped support member on a printing medium having a receptor layers capable of receiving sublimation dyes, and heating the thermal transfer ribbon selectively according to image data.
It is widely well known that a highly gradient color image can be printed easily according to this sublimation dye transfer printing method. However, sublimation materials that are usable for dying by the sublimation dye are limited. Therefore, this method has such a defect that the method is applicable only to limited printing media. Further, sublimation dyes are generally inferior in such image durability as light fastness, solvent resistance, etc. Further, ultraviolet rays exciting type fluorescent dyes excellent in light fastness are not available, as sublimation dyes and therefore, forgery preventive measures must be provided separately.
On the other hand, a thermofusible transfer printing method is for printing a desired image on a printing medium by selectively heating thermal transfer ribbons coated with colored pigments or dyes dispersed in a binder such as resin or wax on a film-shaped support member and transferring colored pigments or dyes on printing media together with a binder.
According to this thermofusible transfer printing method, inorganic or organic pigments that are generally said to have a good light fatness are selectable for coloring materials. Further, resin and wax that are used as a binder are selectable and therefore, solvent resistance can be improved. Basically, any printing media is usable provided that it is adhesive to a binder and printing media in the wide range are selectable and this thermofusible transfer printing method has merits against the sublimation dye transfer printing method.
However, the thermofusible transfer printing method uses a dot area gradation method for the gradation printing by changing transferred dot sizes and therefore, various devises become necessary for multiple gradation printing by accurately controlling dot sizes. For example, there is a method to transfer dots by arranging them in zigzags (hereinafter, this method is referred to as an alternate driving method). When this alternate driving method is used, the heat interference between adjacent heating elements of the thermal print head can be reduced and it can be free from the influence of adjacent pixels. Accordingly, the satisfactory multiple gradation printing becomes possible as dot sizes are accurately controlled.
Further, in order to accurately control dot sizes, the surface of a printing medium must be in satisfactory state but the merit of the thermofusible transfer printing method that is able to select printing media in a wide range is impeded.
So, an indirect transfer printing method is devised to transfer a receptor layer of an intermediate transfer medium on a printing medium after printing multiple gradations on an intermediate transfer medium having a receptor layer of the satisfactory surface. According to this method, when an intermediate transfer medium is adjusted so that it can be transferred on a printing medium, it is not required to select a printing medium and therefore, the multiple gradations can be printed for any printing medium.
However, even for the methods described above, there are problems shown below.
For example, when an image resolution rises, it becomes necessary to control dots to more small sizes. However, a conventional ink ribbon having a more than 1 xcexcm thick ink layer cannot follow a resolution more than 300 dpi and the image quality will be deteriorated.
When the thickness of ink layers of an ink ribbon is reduced to 1 xcexcm or less, it becomes possible to follow a high resolution. However, a conventional thermal print head that forms one pixel by one heating element drives the heating elements alternately, there is such a problem that the central portion of a heating element rises to an excessively high temperature and the ink layers are broken and the image quality is deteriorated.
Further, when the tonal printing is made according to the thermal transfer printing method, especially, by the thermofusible transfer printing method, if the surface smoothness of the platen roller for press fitting the thermal print head, the ink ribbon and a printing medium is low, there is such a problem that the ink layers and the receptor layer of a printing medium are not satisfactorily for the uneven surface of the platen roller and the image quality is deteriorated.
When printing the multi-gradations, the heating elements should be driven alternately and when printing Binary images such as character images, it must be set so as to drive the heating elements similarly to the array of pixels. However, this setting was made by an image processor provided to a printer and there is such a problem that the image processor are complicated and a price becomes high.
Further, black ink for printing binary images such as character images and fluorescent ink for forgery prevention are prepared in the composition differing from color inks that are used for printing multi-gradation images such as face images. In the gray scale of black only and the multi-gradation printing of fluorescent image, the printing was made by an artificial gradation method such as dither or achieved by superimposing color inks. Therefore, there is such problems that the image quality is deteriorated and cost is increased as color ink consumption increase.
It is an object of this invention to provide a thermal transfer printing method capable of printing multi-valued images like highly gradient color images, binary images like character images and fluorescent images that are capable of preventing forgery and alteration in high quality, and a printer system.
According to an embodiment of this invention, there are provided a thermal transfer printing method in a thermal transfer printing apparatus including: a thermal transfer ink ribbon having a 0.4-1 xcexcm thick color thermofusible ink layers formed on a film-shaped substrate member; an intermediate transfer medium having a receptor layer on which ink in the multiple thermofusible color ink layers are transferred from the thermal transfer ink ribbon formed on a film-shaped substrate member; a thermal print head having multiple heating elements arranged in a line so as to form one pixel using at least two heating elements; and a platen roller formed by an elastic material having a rubber hardness more than 80xc2x0 contacting the thermal print head, the thermal transfer ink ribbon and the intermediate transfer medium in the overlapped state, the thermal transfer printing method comprising: forming an image on the receptor layer of the intermediate transfer medium by selectively applying and driving the heating elements of the thermal print head according to image data so as to thermally transfer inks of thermofusible ink layers from the thermal transfer ink ribbon on the intermediate transfer medium; and transferring the receptor layer of the intermediate transfer medium having the formed image on a printing medium under pressure and heat.
Further, according to the embodiment of this invention, there are provided a printer system comprising: a printer including: a thermal transfer ink ribbon having a 0.4-1 xcexcm thick color thermofusible ink layers formed on a film-shaped substrate member; an intermediate transfer medium having a receptor layer on which inks in the multiple thermofusible color ink layers are transferred from the thermal transfer ink ribbon formed on a film-shaped substrate member; a thermal print head having multiple heating elements arranged in a line so as to form one pixel using at least two heating elements; and a platen roller formed by an elastic material having a rubber hardness more than 80xc2x0 contacting the thermal print head, the thermal transfer ink ribbon and the intermediate transfer medium in the overlapped state, and a print controller to control the image printing by selectively powering and driving the heating elements of the thermal print head according to image data, form an image on the receptor layer of the intermediate transfer medium by thermally transferring inks of the thermofusible ink layers of the thermal transfer ink ribbon on the receptor layer of the intermediate transfer medium, and transfer the receptor layer of the intermediate transfer medium with the image formed thereon; and a computer connected to the printer via a two-way communication means and send image data to be printed to the print controller of the printer.